Slight risk (of severe thunderstorms)

Severe thunderstorms are expected to affect between two and five percent of the area. A slight risk generally implies that severe weather events are expected to be isolated.

Smog

Pollution formed by the interaction of pollutants and sunlight (photochemical smog), usually restricting visibility, and occasionally hazardous to health.

Smoke

A suspension in the air of small particles produced by combustion. A transition to haze may occur when smoke particles have traveled great distances (25 to 100 statute miles or more) and when the larger particles have settled out and the remaining particles have become widely scattered through the atmosphere.

Snow

Frozen precipitation composed of ice particles in complex hexagonal patterns. Snow forms in cold clouds by the direct transfer of water vapor to ice.

Snow shower

Snow falling at varying intensities for brief periods of time. Some accumulation is possible.

Snowfall

The depth of new snow that has accumulated since the previous day or since the previous observation.

Snowflake

White ice crystals that have combined in a complex branched hexagonal form.

Special marine warning

Issued for brief or sudden occurrence of sustained wind or frequent gusts of 34 knots or more. This is usually associated with severe thunderstorms or waterspouts.

Squall

A strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots and is sustained at 22 knots or more for at least one minute. In Canada, a squall is defined as a strong, sudden wind which generally lasts a few minutes then quickly decreases in speed. In Australia, it is described as a sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value.

Storm

In marine usage, winds 48 knots (55 miles per hour) or greater.

Temperature

A measure of the warmth or coldness of an object or substance with reference to a standard value.

Thunder

The sound caused by a lightning stroke as it heats the air and causes it to rapidly expand.

Thunderstorm

A storm with lightning and thunder produced by a Cumulonimbus cloud, usually producing gusty winds, heavy rain and sometimes hail. In Australia, they are described to be usually short-lived and hit on only a small area.

Tornado

A violent rotating column of air, in contact with the ground, pendant from a cumulonimbus cloud. A tornado does not require the visible presence of a funnel cloud. It has a typical width of tens to hundreds of meters and a lifespan of minutes to hours.

Turbulence

A warning issued when sustained winds of 39 to 73 miles per hour (34 to 63 knots) are expected within 24 hours.

Typhoon

A hurricane that forms in the Western Pacific Ocean. It is a term used in Australia for a tropical cyclone in the northwestern Pacific with maximum winds above 117 kilometers per hour (63 knots).

Warm front

A narrow transitions zone separating advancing warmer air from retreating cooler air. The air behind a warm front is warmer and typically more humid than the air it is replacing. In Canada, it is defined as the trailing edge of a retreating cold air mass and moves in such a way that the warmer air replaces the colder air.

Wave

In meteorology any pattern identifiable on a weather map that has a cyclic pattern or a small cyclonic circulation in the early stages of development that moves along a cold front. In Canada, A wave, in meteorology, is the intersection of warm and cold fronts.

Wind

Wind is the horizontal movement of air relative to the earth's surface and is caused by variations in temperature and pressure (for instance, air rises as it warms and a cool breeze moves in to take the place of the rising air.) Wind is also known as moving air.

Wind chill

The additional cooling effect resulting from wind blowing on bare skin. The wind chill is based on the rate of heat loss from exposed skin caused by the combined effects of wind and cold. The (equivalent) wind chill temperature is the temperature the body "feels" for a certain combination of wind and air temperature.

Winter storm

A heavy snow event. A snow accumulation of more than six inches in 12 hours or more than 12 inches in 24 hours.